GATE CE 2023 Set 2 — Question 18
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Geotechnical Engineering → Subsurface Investigation → Standard Penetration Test
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Question
A standard penetration test (SPT) was carried out at a location by using a manually operated hammer dropping system with 50% efficiency. The recorded SPT value at a particular depth is 28. If an automatic hammer dropping system with 70% efficiency is used at the same location, the recorded SPT value will be ________.
Correct answer
(B) 20
Solution
The SPT -value is inversely proportional to the energy efficiency of the hammer system used. The relationship between the number of blows () and the efficiency () is given by:Given:
(recorded SPT value)
(manual system efficiency)
(automatic system efficiency)Substituting the values:Thus, the recorded SPT value with the automatic system will be 20.
(recorded SPT value)
(manual system efficiency)
(automatic system efficiency)Substituting the values:Thus, the recorded SPT value with the automatic system will be 20.
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